122 PHYSICAL EXPRESSION. 



jaws is produced by 'the masseter and temporal- 

 muscles ; all these muscles are supplied by the fifth- 

 nerve, and it is to their condition that we must 

 look for information as to the condition of the cen- 

 tral origin of the nerve. Tooth-grinding, when it 

 has become a habit, is indicated by the flattened 

 condition of the tips or edges of the teeth, which may 

 be ground down a sign that may be particularly 

 seen in the incisors and canines. Ground teeth are 

 very common in nervous children, such as those 

 who suffer from recurrent headaches, restless sleep, 

 somnambulism, and finger-twitching. In lunatic 

 asylums and wards for imbeciles it is very common 

 to hear tooth-grinding on every side ; in such cases 

 tooth-grinding is a sign of central irritation of the 

 fifth nerve. It is well to bear in mind that the 

 sensory branches of this nerve supply the membranes 

 of the brain and the external parts of the head. 



Seeing that the slight disturbances occurring- 

 during sleep in many children causes the pterygoids 

 to contract rhythmically, it is not surprising that 

 grave disease should cause spasm of the other 

 muscles supplied by the fifth nerve, as in epilepsy 

 and hysteria. 



The ninth nerve is motor to the tongue, and this 

 organ being a mass of muscular fibres running in 

 various directions almost unsupported by bones, is 

 very sensitive to changes in the nerve-centres. In 

 chorea the tongue is often jerked in and out in a 

 manner quite characteristic of the disease ; in other 

 cases it is easily kept protruded, and its substance 

 is seen to be in a condition of constant movement. 



